The present invention relates to a valve timing control apparatus preferably used for optimizing an open or close timing of at least one of an intake or exhaust valve of an internal combustion engine in accordance with engine operating conditions.
Various valve timing control apparatuses are conventionally used in internal combustion engines for adjusting the rotational phase difference between a crank shaft and a cam shaft. For example, Published Japanese Patent Application No. Kokai 9-32519 discloses one conventional variable valve timing control apparatus for varying a valve timing and/or a lift amount of at least one of intake and exhaust valves by shifting a cam shaft in an axial direction to select a preferable cam profile effective to the associated intake or exhaust valve.